The present invention is directed to non-pathogenic, oncolytic, recombinant polioviruses for the treatment of various forms of malignant tumors. The recombinant polioviruses of the invention are those in which the internal ribosomal entry site (IRES) of the wild type poliovirus was exchanged with the IRES of other picornaviruses, and optionally P1, P3 or the 3'NTR thereof was exchanged with that of poliovirus Sabin type. More particularly, the present invention is directed to the administration of the non-pathogenic, oncolytic, recombinant poliovirus to the tumor directly, intrathecally or intravenously to cause tumor necrosis. The method of the present invention is particularly useful for the treatment of malignant tumors in various organs, such as: breast, colon, bronchial passage, epithelial lining of the gastrointestinal, upper respiratory and genito-urinary tracts, liver, prostate and the brain. Astounding remissions in experimental animals have been demonstrated for the treatment of malignant glioblastoma multiforme, an almost universally fatal neoplasm of the central nervous system.